Mail Server : A host server which holds e-mail messages for clients. The client (the program you use to get your e-mail) connects to the mail server and retrieves any messages that are waiting for you.
From : www.alamedapt.com/alamedanet/glossary.html A mail transfer agent or MTA (also called a mail server, or a mail exchange server in the context of the Domain Name System) is a computer program or software agent which transfers electronic mail messages from one computer to another. From : en.wikipedia.org/wiki/Mail_server